Strip thickness control apparatus



Sept. S, W5 5, P. M DONNELL ETAL STRIP THICKNESS CONTROL APPARATUS Filed June 22, l962 as /40 /44 48 FIRST 38 SECOND 42 THIRD 1 FOURTH TIMER TIMER TIMER TIMER i 50 i w! +24v g A g CONSTANT M CONSTANT CURRENT 4 CURRENT GENERATOR A GENERATOR A Y Y Y' V T I68 T I LOA +24v 24v 64 RELAY 32 d- 9 I I I I, DOWN 28 -30 I g BISTABLE I NULL J I 0EvIc T1 RESET /66 DEVICE q, UP I I I BIAS I BISTABLE VOLTAGE DEV'CE SOURCE T SLOWDOWN |6\ BISTABLE DEVICE l 34 /26 l MOTOR MOTOR CONTROLLER Fig. I

WITNESSES INVENTORS (6 (7 Bernard P. McDonnell Cll'ldl R4944 Loren F. STringer Unite The present invention relates in general to strip thickness control apparatus operative with a strip rolling mill, and more particularly to hot strip mill thickness control apparatus operative for the correction of predictable causes of strip thickness errors, such as for example known temperature changes or ditierences in the metal bar or strip to be rolled.

It is well known in the prior art to provide strip thickness sensing or measuring devices that operate with a rolling mill to determine strip thickness errors by comparing the actual strip thickness rolled by a rolling mill relative to a desired or reference strip thickness. These strip thickness errors can then be converted into control signals suitable for correcting the rolling mill screwdown setting such that subsequently rolled strip will be substantially in accordance with that desired or reference strip thickness. However, it has previously been a problem to provide less expensive and satisfactory corrections for strip thickness or gauge deviations caused by the temperature changes or difierences within the strip to be passed through the rolling mill. These temperature changes may be in the form of a gradual temperature change or rundown or decrease from the head end of a particular strip to the tail end of that strip.

Accordingly, it is an object of this invention to provide improved strip thickness control apparatus which is relatively inexpensive and better operative to control the undesired thickness deviations of a strip rolled by a strip rolling mill.

It is a different object of this invention to provide improved and more simple strip thickness control apparatus which is more economical and will better control the position of the roller members of a strip rolling mill to correct strip thickness errors caused by temperature changes or differences caused by cooling or the like of the temperature material entering the rolling mill.

It is another object of the present invention to provide improved strip thickness control apparatus for better controlling in accordance with a predetermined program the operation of a roller member screwdown setting motor to thereby program as may be desirable to determine the final gauge or thickness of strip material leaving a rolling mill over a greater portion or length of said strip.

These and other objects and advantages of the present invention will become apparent in view of the following description taken in conjunction with the drawings wherein:

FIGURE 1 is a diagrammatic showing of one form of the control apparatus in accordance with the teachings of the present invention;

FIG. 2 is a sketch illustrating the screwdown changes to be made along a strip length;

' FIG. 3 is a sketch illustrating the rolled strip resulting from the operation of the control apparatus in accordance with the teachings of the present invention.

In accordance with the teachings of the present inven- States Pate tion the rolling mill operator programs or predetermines the thickness correction operations in accordance with known temperature characteristics of a bar or strip of material to be rolled in the rolling mill. This is done by predetermining the amount of each of a plurality of screwdown changes and the time sequence of those changes. A hot metal detector or roll force sensing device senses the presence in a predetermined position of a strip to be rolled and initiates the program when that strip is about to or actually enters the rolling mill. This starts a first time delay period after which a first changes in screwdown setting occurs, and a second time delay period is then provided after which a second changes in screwdown setting occurs. This pattern of operation continues for the desired number of changes in the screwdown setting. At the end of the bar or strip, the roller members are returned to their original screwdown setting in readiness for a succeeding bar or strip of material to be rolled.

Thusly, with the use of constant voltage rnotor controllers a programmed positioning operation of screwdown settings is provided on a predetermined time schedule using relatively inexepensive components. Such a control system may be most desirable for rolling mills where economic limitations prevent the utilization of fully automatic and more complex closed loop strip thickness control systems.

In FIG. 1 there is shown a rolling mill 10 having an upper roller member 12 and a lower roller member 14 between which a strip of material 16 passes. A motor 18 is operative with a screwdown mechanism 20 for controlling the spacing between the roller members 12 and 114 as presently Well known to persons skilled in this particular art.

The operation of the motor 18 to provide the predetermined screwdown setting change program in accordance with the teachings of the present invention is controlled by a constant voltage motor controller 26 as will be later explained. The initial spacing is manually established by an operator for the roller members 12 and 14 and thereafter is reset after each pass as determined by a null reset device 28 operative to adjust the null position of a contact arm 30 of potentiometer 32 in a predetermined starting position. The null reset device 28 is: operative with a hot metal detector 34 for so positioning the contact arm 30 when a strip 16 is not positioned to enter or pass through the rolling mill 10.

The hot metal detector 34 is also operative to provide a control signal to an input of a first timer 36 operative to wait for a predetermined first time delay period and then provide an output signal through output terminal 38 for providing a first reset operation of the screwdown motor 18. This first control signal is supplied to an input of a second timer 40, which after a predetermined time delay period supplies a second control signal through output terminal 42. The second control signal energizes an input of a third timer 44 which after a predetermined time delay period provides a third control signal through output terminal 46. This third control signal energizes a fourth timer 48 which after a predetermined timer period supplies through an output terminal 50 a fourth control signal. Each of the terminals 38, 42, 46 and 50 are connected through a common conductor 52 to one of the respective inputs of a first constant current generator 54 and the respective inputs of a second constant current generator 56.

The first constant current generator 54 provides at least one of a plurality of predetermined constant value current signals through respective output diodes to a common conductor 58 operative with a control winding of a Down bistable device such as a magnetic amplifier 60 and a Slowdown bistable device 62. The second constant current generator 56 is similarly operative to provide a least one of a plurality of predetermined constant current signals through respective output diodes and a common conductor 64- to energize a control winding of an Up bistable device 66 and a control winding of the Slowdown bistable device 62. The constant current generators 54 and 56 are operative with respective value determining potentiometers as shown in FIG. 1 for determining the value of each of the constant current signals provided by each of the first constant current generator 54 and the second constant current generator 56.

The constant current generators 54 and 56 and the bistable magamp devices are per se, well known and conventional devices in the prior art knowledge of persons skilled in this particular art.

In this regard, the constant current generators 54 and 56 may be thought of as the equivalent to a like plurality of rheostat current sources each controlled by a series connected relay responsive to one of the respective control signals supplied from the terminals 33, 42, 46 and Stl.

The contact arm 30 of the potentiometer 32 is operative to provide an actual position feedback control signal. In acordance with the screwdown setting of the screwdown device and the operation of the screwdown motor 13 the latter control signal is connected to energize a control winding of the Down bistable device 66, a control winding of the Up bistable device 66 and a control winding of the Slowdown bistable device 62. It should be noted that the latter control winding is always energized in the same direction by the provided directional control circuit regardless of the polarity changes of the control signal supplied by the contact arm 30. The Down bistable device 60 is operative to compare the control signal for the actual screwdown position or setting of the screwdown device 20, as provided by the contact arm 30, with the desired screwdown setting signal supplied by the first constant current generator 54 to a control winding of the Down bistable device 60 and dependent upon the operation of the timers 36, 40, 44 and i8. Thusly, when it is desired to decrease the spacing between the roller members 12 and 14, the Down bistable device 60 will periodically supply screwdown position change signals to the motor controller 26 in accordance with the time period operation of the timers 36, 40, 44 and 48.

Similarly, the Up bistable device 66 is operative to compare the actual screwdown setting of the screwdown device 20 as provided through the control signal supplied by the contact arm 30 with the output control signal received from the constant current generator 56. In this regard the output signals from the Up bistable device 66 are supplied to the motor controller 26 for controlling the changes in the screwdown setting in a direction to increase the spacing between the roller members 12 and 14 and are provided in a time sequence determined by the timers 36, 40, 44 and 48.

When it is desired to slow down the operation of the screwdown motor 18, the Slowdown bistable device 62 will provide an output control signal dependent upon the comparison of the control signals received from the contact arm 30 in acordance with the actual settings of the screwdown device 20 with the control signals received from each of the first constant current generator 54 and the second constant current generator 56. It should be noted in FIG. 1 that a bias or reference operation winding is also provided for the Slowdown bistable device 62 for establishing a desired slowdown pattern.

For some rolling mills it may be desired to initiate the operation of the timer 36 by a roll force sensing load relay 68 instead of the hot metal detector 34. In this regard the roll force sensing load relay 68 responds to the entrance ot a strip 16 between the roller members 12 and 14 to thereby increase the roll force between the roller members 12 and 14-. This provides an initiation signal to begin the time scheduled changes in the screwdown setting in accordance with the teachings of the present invention.

In PEG. 2 there is provided a sketch of a resulting shape of a strip of material in accordance with the prior art knowledge operation of rolling mills. More specifically, a strip 30 is shown with the head end 81 of the strip being substantially smaller in thickness than the tail end 33 of the strip along the illustrated 1,000 feet length of the strip. By dotted lines in FIG. 2 there is illustrated the suggested schedule of screwdown changes to correct and compensate for the input shape of the strip 80.

In FIG. 3 there is shown a sketch of a strip of material 82 rolled in acordance with the teachings of the present invention. It will be noted from the showing of FIG. 3 that the strip 82 has substantially a final uniform thickness throughout its length, however the changes in strip thickness for example between 0.080 inch and 0.110 inch have been greatly exaggerated to illustrate the effect of the screwdown position changes accomplished at the times T through T in accordance with the teachings of the present invention.

The motor controller 26 is essentially a conventional and well known constant voltage type motor controller. When either one of the Down bistable device 60 or the Up bistable device 66 provides an output signal, the motor controller 26 provides a first current signal to the motor 118 to cause the motor to change its operation to a first speed level. Then a second current signal is supplied to the motor 18 to cause the motor to change its operation to a second speed level. A third current signal can be supplied to the motor 18 to cause the motor 18 to arrive at a maximum speed level. When it is desired that the operation of the motor 18 be slowed down, such as for example resulting from an output signal from the Slowdown bistable device 62, the speed of the motor is caused to drop from the maximum speed level one or more intermediate speed levels, and when it is desired to stop the operation of the motor 18 it is then dropped to the stopped operation of the motor.

Thusly, it will be seen in FIG. 1 there are shown the position reference constant current generators 54- and 56 which are Operative to supply reference or control voltage signals to govern the desired position change of the roller members 12 and 14. The magnitude of each control signal from the constant current generators 54 and 56 is preselected by the respective control potentiometers operative with those constant current generators as predetermined by the mill operator in accordance with the desired schedule of screwdown setting changes. As shown in FIG. 1, four such reference control signals can be provided by each of the constant current generators 54 and 56 to control the amount of respective screwdown changes that will be made in a given program for a particular strip of material. The time of initiating each screwdown change signal is controlled by the respective timers 36, 4d, 4d and 48. Each of these timers, it should be understood, can be preset to control the particular time delay period which it provides. The first timer 36 is initiated by the hot metal detector 34 sensing the presence of the strip 16 about to enter the rolling mill 10. The succeeding timers are initiated by the output signal from the preceding timer.

The screwdown setting actual position feedback signal is taken from the potentiometer 32 in accordance with the position of the contact arm 30 as determined by a connection with the motor 18 which in actual practice may be through selsyn transmitter and selsyn receiver devices. The position feedback control signal from the potentiometer 30 is a D.C. voltage proportional to the movement of the roller member 12; relative to the roller member 14 and thusly the screwdown setting. An additional null reset device having a null reference position such as the null reset device 28 can be used to reset the potentiometer 30 to a null or starting position after each bar or strip has passed through the rolling mill N.

The bistable magnetic amplifier devices operate as signal comparator devices such that the desired screwdown position control signal from one of the constant current generators 54 or 56 and the actual position feedback signal from the potentiometer 30 are compared in the illustrated bistable devices to in turn control the constant voltage motor control 26 by means of suitable relays or the like. Separate bistable magamp devices are used for the control in the down direction such as the Down bistable device 69 and in the up direction as the Up bistable device 66, with one or more motor slowdown controlling bistable magamps being provided such as the bistable devices 62 to provide the desired slowdown operation of the screwdown motor 18.

Since the screwdown motor is a shunt DC. motor, the motor control 26 is operative to vary the armature voltage as desired by closing shunt contactors connected across resistor sections to in elfect increase the armature voltage during motor startup. The motor control 26 during motor slowdown varies as desired the armature voltage by decreasing in suitable steps the armature voltage of screwdown motor 18 until a zero armature voltage is provided to stop the motor 18.

In the operation of the bistable magamps or magnetic amplifiers 6t) and 66, the input signal from one of the constant current generators is operative to turn the bistable magamp On and then when the feedback signal from the potentiometer 3t builds up to be comparable to that input signal, the bistable magamp turns Off.

It should be understood that the mill operator will program the desired screwdown setting change operation by selecting the amount of screwdown change he desires at the end of each time period determined by the respective timers 36, 40, 44 and 48. Also, the rolling mill operator can determine the length of the time period provided by suitable adjustment of each of the respective illustrated timers. If desired the control apparatus shown in FIG. 1 may be employed on only one rolling mill stand, such as the rolling mill it), or it may be employed on more than one such rolling mill stand. When the first timer 36 is energized by the hot metal detector 34 sensing the presence of a strip 16 about to pass between the roller members 12 and 14, the timing cycle commences and after a preset time delay determined by the first timer 36, a preselected one of the constant current generators 54 and 56 will provide a first predetermined constant current position control signal to cause the screwdown motor 18 to make a first predetermined change in the screwdown setting of the rolling mill 10. Then as the second timer t0 completes its predetermined time delay period it causes the same or even a diiferent one of the constant current generators 54 and 56 to make a second change in the spacing between the roller members 12 and 14 by suitable control of the screwdown motor 18. This repeated operation continues for the desired number of preset screwdown changes for each particular strip of material passing between the roller members 12 and 14. At the end of a given strip of material, one of the hot metal detector 34 or load sensing relay device 68 will cause the timers to reset. Since the appropriate magamp oil or 66 will respond to the signal from the potentiometer 3% to move the screwdown motor 18 to drive to zero this latter signal, the spacing between the roller members 12 and 14 is in this manner caused to return to the desired original roller member spacing through the operation of the null reset device 28. The null reset device 28 is caused to operate by the hot metal detector 34 sensing the absence of a strip about to enter the rolling mill 10 to provide a suitable control signal for the null reset device for causing the contact arm 30 to assume a starting reference or null position. This introduces a feedback signal to the proper one of the Down bistable magamp 60 or the Up bistable device 66 for causing the motor controller 26 to so control the screwdown motor 18 to return the screwdown mechanism 20 to the desired original operating position, and this drives the feedback signal to zero.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope and the spirit of the present invention.

We claim as our invention:

1. In thickness control apparatus for strip material passing through a rolling mill having first and second roller members, the combination of motor means operative with at least one of said roller members for controlling the spacing between said roller members, strip position sensing means for providing a first control signal when said strip material is sensed in a predetermined position relative to said rolling mill, first control means responsive to said first control signal for beginning a first time delay period and thereafter providing a second control signal, second control means responsive to said second control signal for beginning a second time delay period and thereafter providing a third control signal, and third control means operative with said motor means for effecting a first predetermined change in the spacing between said roller members in response to said second control signal and for etfecting a second predetermined change in the spacing between said roller members in response to said third control signal.

2. In thickness control apparatus for strip material passing through a rolling mill having first and second roller members, the combination of a motor operative with at least one of said roller members for controlling the spacing between said roller members, strip sensing means for providing a first control signal when the presence of said strip material is sensed at a predetermined location relative to said rolling mill, first motor control means responsive to said first control signal for providing a plurality of second control signals in succession after respective predetermined time delay periods and after the occurrence of said first control signal, second motor control means operative with said motor for effecting a predetermined change in the spacing between said roller members in response to each of said second control signals, and reset control means operative with said strip sensing means and responsive to the absence of said strip material at said location for controlling said motor to provide a predetermined reset spacing between said roller members.

3. In thickness control apparatus for strip material passing through a rolling mill having first and second roller members, the combination of motor means operative with at least one of said roller members for controlling the spacing between said roller members, strip position sensing means for providing a first control signal when said strip material is sensed, a plurality of time period providing means responsive to said first control signal for providing a plurality of successive motor control signals in accordance with a predetermined time schedule, and motor control means operative with said motor means for effecting a like plurality of predetermined changes in the spacing between said roller members in response respectively to said plurality of motor control signals.

4. In thickness control apparatus for strip material having a known temperature characteristic and passing through a rolling mill having firt and second roller members, the combination of motor means operative with at least one of said roller members for controlling the spac- 7 8 ing between said roller members, strip position sensing References Cited by the Examiner means for providing a first control signal when said strip UNITED STATES PATENTS material is sensed, a plurality of time control devices successively responsive to said first control signal and each 2,989,717 10/59 HEIRS et 8O 56'1 providing a motor control signal after a predetermined 5 2,932,626 4/60 611901163 at EEG-562 time delay period, and motor control means operative 2,983,043 5/61 f 8G56-1 3,035,465 5/62 DiNicolantonio et al. 80-562 with said motor means for effecting successive predetermined changes in the spacing between said roller members l in response respectively to said motor control signals and CHARLES LANHAM y Emmme" in accordance with said temperature characteristic. NEDWEN BERGER, Examiner. 

2. IN THICKNESS CONTROL APPARATUS FOR STRIP MATERIAL PASSING THROUGH A ROLLING MILL HAVING FIRST AND SECOND ROLLER MEMBERS, THE COMBINATION OF A MOTOR OPERATIVE WITH AT LEAST ONE OF SAID ROLLER MEMBERS FOR CONTROLLING THE SPACING BETWEEN SAID ROLLER MEMBERS, STRIP SENSING MEANS FOR PROVIDING A FIRST CONTROL SIGNAL WHEN THE PRESENCE OF SAID STRIP MATERIAL IS SENSED AT A PREDETERMINED LOCATION RELATIVE TO SAID ROLLING MILL, FIRST MOTOR CONTROL MEANS RESPONSIVE TO SAID FIRST CONTROL SIGNAL FOR PROVIDING A PLURALITY OF SECOND CONTROL SIGNALS IN SUCCESSION AFTER RESPECTIVE PREDETERMINED TIME DELAY PERIODS AND AFTER THE OCCURRENCE OF SAID FIRST CONTROL SIGNAL, SECOND MOTOR CONTROL MEANS OPERATIVE WITH SAID MOTOR FOR EFFECTING A PREDETERMINED CHANGE IN THE SPACING BETWEEN SAID ROLLER MEMBERS IN RESPONSE 